As a preprocessor of the automatic speech recognizer in a noisy environment, a microphone array system has been investigated to reduce the environmental noise. In usual microphone array design, a plane wave is assumed for the sake of simplicity (far-field assumption). However, this far-field assumption does not always hold, resulting in distortion in the array output. In this report, the subspace method, which is one of the high resolution spectrum estimator, is applied to the near-field source localization problem. A high resolution method is necessary especially for the near-field source localization with a small-sized array. By combining the source localization technique with a spatial inverse filter, the signal coming from the multiple sources in the near-field range can be separated. The modified minimum variance beamformer is used to design the spatial inverse filter. As a result of the experiment in a real environment with two sound sources in the near-field range, 60-70% of word recognition rate was achieved.

This study is to clear how the impedance and the current of a simple printed line model involve to the near field electromagnetic noise radiation, by computer simulation and experiment. Frequency characteristics of the impedance and the current of the printed line and the near field noise are considered, from low to high frequency components. The model size 225 60 0.51 mm3, length of the line is 185 5 mm2 and 1 kΩ termination resistance is connected as non-matching load. FDTD method is used to calculate the impedance, the current waveform and the near field noise. Measurements of the line impedance and the near field noise spectrum by clock pulse are compared with simulations. It is cleared that using FDTD method, the characteristic of impedance of the printed line model, the current waveform, and the near field noise can be calculated at the same simulator. As results, from calculation and measurement, the near field noise has a relationship with impedance of printed line model. Emission at frequency less than 200 MHz, which is near the wavelength of λ/4, is observed at significant intensity. So, it is suggested that near field noise emission should be discussed from low to high frequency and analysis of the characteristics of the printed line and magnetic near field noise using FDTD method and measurement is useful to basic examination of complex PCB models.

Theoretical values of site attenuation for broadband receiving antenna or the antenna factor of broadband antenna over the frequency range from 30 MHz to 1 GHz have been calculated or measured by some researchers. For a frequency range over 1 GHz, wire antennas or horn antennas should be used. However, the theoretical site attenuation or antenna factor over 1 GHz have never yet been calculated. A CLS (Conical Log-periodic Spiral) antenna is generally used for EMC/EMI measurements in the microwave band as a broadband wire antenna for the swept frequency method. However, this antenna has the defect that its use results in the loss of polarization information. So we proposed an improved CLS antenna which has linear polarization. This new CLS antenna has another wire wound symmetrically to that of the standard CLS antenna. For this reason, we named it a double-wire CLS antenna. The double-wire CLS antenna loses no polarization information. We calculated the height pattern and the frequency characteristics of CSA (Classical Site Attenuation) for the double-wire CLS antenna when used for receiving, or used for both transmitting and receiving, as well as the antenna factor. Moreover, NSA (Normalized Site Attenuation) when the double-wire CLS antenna is used for receiving or used for both transmitting and receiving in free space were calculated.

The coupling response of an external transient electromagnetic field to a transmission line is considered. An experiment has been conducted to verify the line equations for a transmission line excited externally by a transient near field. The model field is generated by a monopole antenna installed in the vicinity of the transmission line and driven by a step waveform. The waveform is analyzed into discrete spectrum components using a Fourier transform. The frequency-domain field components affecting the transmission line are estimated by the moment method, and then the induced frequency-domain voltage at the terminal load is converted into a time-domain voltage using an inverse Fourier transform. Comparison between the measured and the computed values provides verification of the line equations. The coupling mechanism is discussed from the experimental results. It seems equivalently that the transmission line picks up the field, generated at the feed point and the top point of the monopole antenna, at both terminal ends.

New series expressing the radiation fields from both axial and circumferential slots on a circular conducting cylinder are derived. These new series converge rapidly even for near fields. This letter includes useful figures showing characteristics of near fields calculated numerically using the new series.

To increase the accuracy of a near field antenna measurement system, it is necessary to know radiation characteristics of a probe to detect near field data. Open ended waveguide used as a near field probe in our system was analyzed using Transmission Line Matrix (TLM) method which is a time domain electromagnetic solver. Validity of this analysis has been confirmed by comparison with experimental data and existing theoretical approximation. Frequency dependence of a complex reflection coefficient at the waveguide aperture has been derived and is shown to agree with measured values. The radiation pattern of the open ended waveguide with mounting structure is also calculated. Ripples on both the amplitude and phase patterns are correctly predicted by our simulation. This method can be applied to accurately model the effect of probe antennas to enhance the accuracy of near field antenna range.

An estimation method for efficiently calculating the field intensity in the Fresnel region of broadside colinear array antennas is developed, and its performance is experimentally verified. The calculation utilizes only the antenna design data, and is readily applicable to arbitrary array antennas. This method can provide a safety protection zone in the proximity of array antennas, in order to protect radio communication personnel and general public from the potentially hazardous radiofrequency exposure.

This paper presents an analysis of the dose rate in tissue irradiated by an electromagnetic near field of a circular loop antenna. An analytical model comprised of a circular loop antenna located in the vicinity of the semi-infinite plane of a homogeneous biological medium was formulated. A quasi-static hypothesis was not introduced. The theoretical formulation was rigorously developed based on Maxwell equations which used an electric vector potential, cylindrical coordinates and a Hankel transform. The internal electric field E and the specific absorption rate (SAR) were adopted as indices for the dose in the tissue. This formulation was applied to the dosimetry of a high-frequency therapeutic device (HFTD) and experiment of irradiation to a frog web. The frequency of the applied electro-magnetic fields (EMF) was 9-10MHz. The distance between the antenna and tissue was 2.0-3.2mm. The dose of HFTD were 0.75V/m and 0.35mW/kg, respectively. The dose of experiment of the irradiation to a frog web were 0.42-2.08V/m and 0.11-2.69mW/kg, respectively. The SAR values obtained by this analysis were small enough to conclude that the effects were non-thermal. The calculated SARs of these experiments were compared with estimated SARs in experiments on calcium efflux change due to a weak modulated RF field. All were found to be of the same order of magnitude.